The invention relates generally to film capacitors, and more particularly, to high capacitance film capacitors.
Over the last decade, significant increases in capacitor reliability have been achieved through a combination of advanced manufacturing techniques and new materials. Film capacitors can be classified into three types based on the manufacturing technology, namely, film and foil capacitors, metallized film capacitors and mixed technology film capacitors.
Generally, film and foil capacitors consist of two metal foil electrodes separated by a layer of plastic film. One of the commonly used plastic films is polypropylene. Typically, a film and foil capacitor is made by alternating two pieces of aluminum foil with two layers of plastic film. These interleaved layers are wound around a spindle in a manner that prevents the metal layers from touching each other. The film and foil capacitors have been widely used in high power and utility industry due to high current handling capability. Metallized film capacitors differ from the film and foil capacitors in the sense that the aluminum foils are replaced by a layer of metal film that is vacuum deposited onto the layer of plastic film. The metal film layer is typically extremely thin, in the order of about 50-500 angstroms and is typically aluminum or zinc. The metallized capacitor has the advantages of fail-safe characteristic, low equivalent series resistance, size, simplicity, and cost of manufacturing. Mixed technology capacitors are a combination of both film and foil capacitors, and metallized film capacitors. Typically, these are high voltage capacitors.
While significant improvements have been made in capacitors in the past few decades, certain issues continue to exist, for example low surface area and restriction in thickness of film that leads to a low capacitance. Therefore, it would be desirable to design a film capacitor that would address the aforementioned problems and meet the current demands of industry applications.